sphinx: import docs

The Yocto Project docs was migrated from Docbook to Sphinx in YP
 3.2. This 3.1 is an LTS release, and since 3.1 docs are 'close to'
 the docs in 3.2, we agreed to backport sphinx docs onto 3.1.

This first patch brings all changes done in 3.2 until:
7f64574f7 README: include detailed information about sphinx

There are other changes after this commit, but they will be
 selectively backported in individual patches.

This patch was generated with the following command:

git cherry-pick -n \
 $(git log --reverse --oneline \
 ac352ad7f95db7eeacb53c2778caa31800bd7c26..7f64574f7 \
| cut -f1 -d' ')

The following commits were applies in the dunfell docs, but not in
master, so they were first reverted (and squashed into this change). A
commit will reintroduce the content from these patches in the Sphinx
files in a followup patch.

069c27574 Documenation: Prepared for the 3.1.1 release
bd140f0f9 Documentation: Add 3.1.1 version updates missing from previous commit
17cc71a8f Documenation: Prepared for the 3.1.2 release
1a69e2c02 Documenation: Prepared for the 3.1.3 release
8910ac1c7 Documenation: Prepared for the 3.1.4 release

(From yocto-docs rev: c25fe058b88b893b0d146f3ed27320b47cdec236)

Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/conf.py

@@ -0,0 +1,127 @@
+# Configuration file for the Sphinx documentation builder.
+#
+# SPDX-License-Identifier: CC-BY-2.0-UK
+#
+# This file only contains a selection of the most common options. For a full
+# list see the documentation:
+# https://www.sphinx-doc.org/en/master/usage/configuration.html
+
+# -- Path setup --------------------------------------------------------------
+
+# If extensions (or modules to document with autodoc) are in another directory,
+# add these directories to sys.path here. If the directory is relative to the
+# documentation root, use os.path.abspath to make it absolute, like shown here.
+#
+import os
+import sys
+import datetime
+
+current_version = "dev"
+
+# String used in sidebar
+version = 'Version: ' + current_version
+if current_version == 'dev':
+    version = 'Version: Current Development'
+# Version seen in documentation_options.js and hence in js switchers code
+release = current_version
+
+
+# -- Project information -----------------------------------------------------
+project = 'The Yocto Project'
+copyright = '2010-%s, The Linux Foundation' % datetime.datetime.now().year
+author = 'The Linux Foundation'
+
+# -- General configuration ---------------------------------------------------
+
+# to load local extension from the folder 'sphinx'
+sys.path.insert(0, os.path.abspath('sphinx'))
+
+# Add any Sphinx extension module names here, as strings. They can be
+# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
+# ones.
+extensions = [
+    'sphinx.ext.autosectionlabel',
+    'sphinx.ext.extlinks',
+    'sphinx.ext.intersphinx',
+    'yocto-vars'
+]
+autosectionlabel_prefix_document = True
+
+# Add any paths that contain templates here, relative to this directory.
+templates_path = ['_templates']
+
+# List of patterns, relative to source directory, that match files and
+# directories to ignore when looking for source files.
+# This pattern also affects html_static_path and html_extra_path.
+exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store', 'boilerplate.rst',
+                    'adt-manual/*.rst']
+
+# master document name. The default changed from contents to index. so better
+# set it ourselves.
+master_doc = 'index'
+
+# create substitution for project configuration variables
+rst_prolog = """
+.. |project_name| replace:: %s
+.. |copyright| replace:: %s
+.. |author| replace:: %s
+""" % (project, copyright, author)
+
+# external links and substitutions
+extlinks = {
+    'yocto_home': ('https://yoctoproject.org%s', None),
+    'yocto_wiki': ('https://wiki.yoctoproject.org%s', None),
+    'yocto_dl': ('https://downloads.yoctoproject.org%s', None),
+    'yocto_lists': ('https://lists.yoctoproject.org%s', None),
+    'yocto_bugs': ('https://bugzilla.yoctoproject.org%s', None),
+    'yocto_ab': ('https://autobuilder.yoctoproject.org%s', None),
+    'yocto_docs': ('https://docs.yoctoproject.org%s', None),
+    'yocto_git': ('https://git.yoctoproject.org%s', None),
+    'oe_home': ('https://www.openembedded.org%s', None),
+    'oe_lists': ('https://lists.openembedded.org%s', None),
+}
+
+# Intersphinx config to use cross reference with Bitbake user manual
+intersphinx_mapping = {
+    'bitbake': ('https://docs.yoctoproject.org/bitbake/', None)
+}
+
+# -- Options for HTML output -------------------------------------------------
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+#
+try:
+    import sphinx_rtd_theme
+    html_theme = 'sphinx_rtd_theme'
+    html_theme_options = {
+        'sticky_navigation': False,
+    }
+except ImportError:
+    sys.stderr.write("The Sphinx sphinx_rtd_theme HTML theme was not found.\
+    \nPlease make sure to install the sphinx_rtd_theme python package.\n")
+    sys.exit(1)
+
+html_logo = 'sphinx-static/YoctoProject_Logo_RGB.jpg'
+
+# Add any paths that contain custom static files (such as style sheets) here,
+# relative to this directory. They are copied after the builtin static files,
+# so a file named "default.css" will overwrite the builtin "default.css".
+html_static_path = ['sphinx-static']
+
+html_context = {
+    'current_version': current_version,
+}
+
+# Add customm CSS and JS files
+html_css_files = ['theme_overrides.css']
+html_js_files = ['switchers.js']
+
+# Hide 'Created using Sphinx' text
+html_show_sphinx = False
+
+# Add 'Last updated' on each page
+html_last_updated_fmt = '%b %d, %Y'
+
+# Remove the trailing 'dot' in section numbers
+html_secnumber_suffix = " "